This invention relates to an improved process for the production of epichlorohydrin i.e., -chloropropylene oxide. Conventionally epichlorohydrin is produced by the dehydrohalogenation of dichlorohydrin. The dichlorohydrins i.e., 2,3 dichloro-1-propanol and 2,3 dichloropropanol, herein collectively called dichlorohydrin, may be prepared by reacting chlorine, water and allyl chloride in high dilution of e.g., 250 to 400 volumes of water per volume of e.g., halohydrocarbon as disclosed in U.S. Pat. No. 2,714,121, incorporated by reference.
It is known from U.S. Pat. No. 2,177,419, incorporated herein by reference, that epichlorohydrins such as epichlorohydrin may be prepared by reacting a dihalohydrin with a basic substance in the presence of water and rapid separation of the product from the reaction mixture by flash distillation, to minimize formation of other organic compounds.
A disadvantage of such processes is that after removal of the epichlorohydrin product there remains a substantial quantity of water containing a considerable concentration of inorganic salts and smaller but significant quantities of organic compounds. particularly halogen-containing organics such as tetrachloropropyl ether, trichloropropane and the like which must be removed prior to discharge to receiving bodies of water such as rivers and lakes.
It has now been found that advantages selectivity to the desired epichlorohydrin can be retained while reducing the amount of water consumed in the process, and enabling significant reduction in the quantity of aqueous waste that must be treated by using a sequence of electrodialysis and reverse osmosis steps to separate undesirable materials from the final reaction mixture, and recycling a portion of the permeate thus obtained to the dichlorohydrin reaction zone.